This invention relates to a wellhead safety valve control system and, more particularly, to a wellhead safety valve control system used for closing a surface safety valve(SSV) and a subsurface safety valve(SCSSV) in a controlled sequence and to dump valves used as components of the system used for achieving the valve shutdown.
In our U.S. Pat. No. 5,291,918 dated Mar. 8, 1994 and entitled SAFETY VALVE ACTUATOR ASSEMBLY, there is disclosed a safety valve actuator used for closing a gate valve in a flowline and a hydraulic circuit which schematically illustrates the flow of hydraulic fluid in the circuit.
Improvements have been made, however, to overcome some of the disadvantages of the apparatuses taught in the ""918 patent. One disadvantage of such apparatuses is that no provision was made for pressure relief. It is possible for fluid in the control circuit to increase or decrease in volume as the ambient temperature increases or decreases and provision should be made to allow for pressure relief in the event that the components are required to handle the pressure created by the increased fluid volume.
Other advantages in the present invention will become apparent during the detailed description and explanation made hereafter.
According to one aspect of the invention, there is provided a wellhead safety valve control system for opening and closing a surface controlled safety valve and a surface controlled subsurface safety valve, said system comprising a first dump valve and a first safety valve circuit operably associated with said surface controlled safety valve, a second dump valve and a second safety valve circuit operably associated with said surface controlled subsurface safety valve, an SSV trip control circuit operably associated with said first dump valve, an SCSSV trip control circuit operably associated with said second dump valve, a pump operably associated with said first and second safety valve circuits and at least one check valve to operably isolate said SCSSV trip control circuit of said second dump valve from said SSV trip control circuit of said first dump valve.
According to a further aspect of the invention, there is provided a method of sequentially or individually closing a surface safety valve and a subsurface safety valve, said method comprising monitoring the pressure of said flowline with a pilot circuit, opening a trip valve when said pressure falls outside of a predetermined range, exhausting fluid within said pilot circuit to a reservoir when said trip valve is opened, reducing the pressure of fluid within a first dump valve during the exhaustion of fluid from said pilot circuit to said reservoir and opening said first dump valve and closing said surface safety valve.
According to yet a further aspect of the invention, there is provided a method of opening subsurface and surface safety valves, said method comprising pumping fluid at a first pressure to a second dump valve operably associated with said subsurface safety valve to thereby close said second dump valve, continuing said pumping to increase pressure in an SCSSV safety valve circuit to open said subsurface safety valve, closing a first dump valve, pumping fluid at a second pressure to increase pressure in said first dump valve and in an SSV safety valve circuit, opening said surface safety valve by said increased pressure, monitoring the pressure in said flowline within predetermined limits with a pilot, opening said first dump valve when said pressure in said flowline falls outside said predetermined limits and closing said surface safety valve when said first dump valve is opened.
According to still yet a further aspect of the invention, there is provided a dump valve for controlling the opening and closing of a safety valve, said dump valve comprising a body, a piston movable within said body, a dump valve poppet on said one side of said piston, an inlet port to supply fluid to one side of said dump valve poppet, an exit port to allow fluid egress on the opposite side of said dump valve poppet, and a pushrod operable on said dump valve poppet and movable by said piston to open said dump valve poppet and allow fluid flow from said one side to said opposite side of said dump valve.
According to still yet a further aspect of the invention, there is provided a method of closing a subsurface safety valve comprising reducing pressure in an SCSSV trip control circuit operably associated with a second dump valve, opening said second dump valve by said reduction of pressure in said SCSSV trip control circuit, exhausting fluid from an SCSSV safety valve circuit operably associated with said subsurface safety valve through said second dump valve to a SCSSV return tank and thereby closing said subsurface safety valve.